is it acceptable if IQ/OQ is performed by the third party without been witnessed by the user?
IQ/OQ can be performed by the third party but in the presence of the user.
In my experience you can purchase a written PQ from the manufacturer. Combined with other appropriate documents, it will serve as a validation package for the equipment which is needed to validate the EM program for the facility.
What is EM program?
It can be acceptable if you have given authorization to the third party to conduct IQ/OQ on your behalf.
Provided the Service provider should have trained staffs,certification or accredited, audited and approved facility, use of calibrated and validated standards, follow GMP Norms.